Generally, a combustion method of gaseous fuel includes a premixed combustion in which gaseous fuel and combustion air are premixed to be supplied to a combustion chamber, a diffusion combustion in which fuel and air are separately supplied, and a partially premixed combustion which is a hybrid between a premixed combustion and a diffusion combustion.
The partially premixed combustion is referred to a combustion performed by a Bunsen burner. The Bunsen burner premixes and supplies a primary air, which is a part of air being supplied, with fuel, and separately supplies secondary air to a flame generation portion, thereby inducing a complete combustion. With advantages of flame stability and low generation possibility of a backfire phenomenon and the like, the Bunsen burner is mainly employed in a combustion apparatus including a typical boiler for home use and the like.
However, since flame of the burner is long and a flame temperature is high due to a structure of the Bunsen burner and also an amount of air required for a combustion is excessively needed more than a theoretical amount of air, heat loss is large due to an exhaust gas of a high temperature and also an exhaust amount of NOx and CO is large so that the Bunsen burner has limitation regarding an efficiency maximization and a pollutant reduction of a combustion apparatus.
As one of combustion methods for reducing a generation amount of NOx, a rich-lean combustion is known in the related art.
Forming simultaneously a fuel rich combustion having a low excess air ratio and a fuel lean combustion having a high excess air ratio in a premixed combustion by avoiding a condition in which a ratio between fuel and excess air at a highest flame temperature is 1, the rich-lean combustion lowers a flame temperature to reduce a generation amount of NOx, and also flame resulting from the fuel rich combustion serves to stabilize an instability phenomenon such as a flame fluttering and the like which may occur while the fuel lean combustion takes place.
An example of a combustion apparatus of such a rich-lean combustion method is disclosed in Korean Registered Patent No. 965277.
However, the combustion apparatus disclosed in Korean Registered Patent No. 965277 is provided with nozzles for supplying a rich mixture and a lean mixture, respectively, so that a structure thereof is complicated due to a plurality of components and there is a problem in which air is not uniformly supplied because some of air supplied from a ventilator is supplied through a hole formed at a partition plate.